The present invention relates to the casing for packing lunch boxes and Sushi packages sold in station Kiosks and other food packages available in supermarkets and fast food shops.
According to the method of creating these types of packages, known in the prior art, various types of plastic sheets, such as semi-hard, solid or foamed, single layered or multi-layered sheets, are sheet-formed by suitable methods, e.g., vacuum forming, pneumatic forming and hot pressing, thereby predetermined preferred shapes are obtained. The materials of these packages consist, for example, of polystyrene, polypropylene, polyethylene, polyvinyl chloride and other plastics. According to other methods for forming the packages based on the prior art include injection molded plastics which small wall thickness and sheet-formed ones with water-proof or oil-proof paper material through hot pressing.
Some casings for packing, used in the marketplace at present, are equipped with lids. These lids are attached to the fringe of the opening in the main body of the casing. The structure of this mounting is shown in FIG. 3.
Around the opening of casing main body 1, fringe 1a is protruded outwardly. In the outer periphery of lid 2, fringe 2a is formed while covering fringe 1a from the upper part. Fringe 2a is provided with inwardly faced engaging projections 2b that can engage with the lower face or lower edge of fringe 1a along the entire length of fringe 2a or at several locations in suitable intervals. Fringe 1a engages with engaging projections 2b to fix the lid onto casing main body 1.
Such holding, considerably secured, is advantageous in that the lid is not easily opened from the packing casing. However, its disadvantage is that the lid is not easily opened manually as set forth in detail in the following.
Referring to FIG. 3, opening of lid 2 is effected as follows. Fringe 2a of the lid covers fringe 1a of casing main body 1. Therefore a person's finger cannot grip fringe 1a. Consequently, the side wall of the casing main body should be gripped and fixed with one hand, while a part of fringe 2a is extended with thumb A and forefinger B of the other hand, as shown by the chain lines in FIG. 3. Thereby, the engaged part with fringe 1a is disengaged by deflection. At that time, the part where fringe 2a is disengaged is extremely local. Therefore, the entire body of lid 2 cannot be removed so easily from casing main body 1. If lid 2 is attempted forcefully to be removed from casing main body 1, lid 2 or casing main body 1 is torn or deformed unrecoverably. In other disadvantageous circumstances, the casing itself is so largely deformed that the layout of the housed foods comes in disorder or the casing may be dropped from the hands.
In order to prevent such disadvantages, the part engaged with casing main body 1 must be sequentially and locally disengaged by bending and widening consecutively along the edge of fringe 2a of lid 2, in suitable intervals. However, such operations require a very long time and tedious labor for opening the lid. The foregoing disadvantages become more significant where casing main body 1 is formed in a shallow tray that cannot be securely gripped for opening the lid.